An occasionally irregular blog about orthodontics

October Research update, Part I, Temporary Anchorage Devices

By on October 14, 2013 in Clinical Research, Trials with 0 Comments
October  Research update, Part I, Temporary Anchorage Devices

Temporary anchorage devices

This has been a bumper month for good quality research and I am going to summarise the clinical research in a couple of postings. The first paper concerns a study of temporary anchorage devices and is from the European Journal of Orthodontics.

It is interesting that these have been used for a fair amount of time and are becoming an integral part of the armamentarium of most orthodontists.  I first became aware of the potential for implants as anchorage units, a long time ago in 1987 when I saw a case presented at a meeting in Birmingham, UK in which a canine had been retracted a large distance against a dental implant.  Technology has moved a long way since then and there are many forms of temporary anchorage device available, however, there is still a dearth of good clinical trials that have evaluated their effectiveness.  This paper was interesting and will add some knowledge on this technique.

This is by a team from the University of Connecticut.  In this study they evaluated the effectiveness of temporary anchorage devices when compared to a form of mechanics designed to increase posterior anchorage.  I thought that this was an interesting comparison as they really raised a question about anchorage preparation and careful treatment mechanics versus temporary anchorage devices.  This is relevant to current practice because it is becoming increasingly common, when I am discussing treatment plans with postgraduate students, that when we discuss the need for anchorage, the solution is often “we will place a TAD” instead of “prepare and manage anchorage with our appliances”.  You may now be thinking that I am getting old fashioned, however, we must not forget that good careful mechanics is an important part of anchorage management and even though new technologies are available, they are not necessarily the answer to all our difficulties.  So, what does “old Professor O’Brien” make of this paper?

Temporary-Anchorage-Devices-TADS-Austin-OrthodontistA prospective comparative study between differential moments and miniscrews in anchorage control

A Davoody et al. European Journal of Orthodontics 35 (2012) 568-576.




This was a simple study in which the investigators aimed to compare the effectiveness of a type of temporary anchorage device and a method of anchorage management called the  “differential moment approach”.  The primary outcome measure was molar anchorage loss.  Ninety patients who required extractions of first premolars and overjet reduction were enrolled in the study. The  patients were divided into two groups by allocating the first patient by coin toss and then every following patient was allocated to every other group in order of presentation.  This is not a good way of allocating patients to a trial because it is not possible to conceal the allocation sequence. It was not clear why they followed this method.  Unfortunately, this would put this study at high risk of bias when it is considered for inclusion into systematic reviews.

The “differential moment approach” was a form of mechanics that involved placing a 016×022 ss base archwire with a pre fabricated 017×025 Ni Ti intrusion arch placed into first molar auxiliary tubes and tied to the later incisors over the base archwire.  This resulted in tip back on the molars. The canines were then retracted with springs. When the canines were class I the overjet was reduced with a mushroom looped arch.  The patients who were allocated to a TAD had a spring placed from the TAD to the canine hook and the teeth were retracted on a 016×022 ss wire.

Tooth movement was measured from cephalometric radiographs.  The statistical analysis was a simple univariate analysis.  There were several measurements taken and I shall just concentrate on the clinically important ones (in my opinion).  It appeared that molar tooth movement with the TADS group was 3.2mm better than the differential moment approach and there were minimal differences in incisor position.  Interestingly, with the TAD group there was some distal movement of the upper molars and they suggested that this was caused by bracket binding as the arch wire slid distally through the molar tubes.

The authors also pointed out that there was a high attrition rate to this study and the examiners were not blinded to the treatment allocation.  Again suggesting that this study was at high risk of bias.  Unfortunately, it was not written up to the CONSORT guidelines and this was unusual to see.


So, what do I make of this study?  My feeling is that the authors attempted to answer a simple question. However, the study is at high risk of bias because of the poor allocation concealment and lack of blinding of the examiners who recorded the data.  I also wonder if the study could have been improved if they had enrolled a group of patients who were treated with another form of anchorage reinforcement, for example, a palatal arch or headgear.  This would then help provide information on whether the “differential moment approach” was an effective method of anchorage reinforcement.

Nevertheless, this paper does illustrate that when TADS are used there is little loss of posterior anchorage and continues to add to the information that is becoming available on this technique.

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